1. Field of the Invention
This invention relates in general to circuit interruption apparatus and more particularly to an improved and more economical circuit breaker adapted for use at either the top or bottom of a panelboard.
2. Summary of the Prior Art
Panelboards comprise cabinets in which a source of electrical power is connected through one wall to a main circuit breaker which extends the power through downstream circuit breakers to respective loads. It is often desirable to extend the source of electrical power through the top wall of the panelboard to the main circuit breaker. In this case the main circuit breaker is located adjacent the top of the panelboard for feeding the downstream breakers located therebelow. Extending the source of power through the top wall of the panelboard however may not be the most convenient or economical practice since the source may be more conveniently introduced through the bottom wall of the panelboard.
On the other hand the main circuit breaker is usually constructed with a pivoted handle indicating the ON position of the breaker, when located adjacent the top of the panelboard, by pointing upward at the top limit of handle movement. Locating the main circuit breaker at the bottom of the panelboard on the other hand causes the handle to point downward when in the ON position due to the reversal of the normal limit positions of the breaker handle. The handle of a breaker at the bottom of the panelboard therefore indicates the ON position when the circuit breaker is actually OFF and indicates the OFF position when the circuit breaker is ON thereby contributing to a hazardous situation.
Underwriters' Laboratories has therefore required that pivoted circuit breaker handles either indicate the ON position by pointing upwardly or that the handle be movable horizontally so as not to mislead the operator as to the actual condition of the breaker. The requirement that the circuit breaker handle point up, limits the versatility of such circuit breaker for use in a so called bottom feed panelboard in which the supply is extended through the bottom wall. The sidewise or horizontal movement of the handle, however, is difficult to provide economically, as horizontal movement requires the handle and blades to pivot in directions transverse to each other instead of in parallel directions as is conventionally done.
Conventional circuit breakers often permit the handle to be moved to the OFF position and retained there even if the contacts are welded closed, since the blade closing springs interconnecting each blade with a trip bar may yield to the movement without causing the welded contacts to open. This condition is also misleading and can be dangerous as the operator may believe the circuit is open when it is in fact closed.
In addition circuit breakers commonly employ long distances between the blade pivot and the contacts in order to provide sufficient mechanical force to open the contacts quickly and to permit blow open forces to also open the contacts. Long blades in turn require substantial copper which is expensive.